This invention relates to sterilizing with a mixture of ethylene oxide and an inert gas and, more specifically, to the use of such mixture for an indefinite number of successive sterilization cycles.
Ethylene oxide gas is widely used as a sterilizing agent in spite of its known problems of flammability, as described in Industrial and Engineering Chemistry, June 1950, at pages 1251-1258. For this reason, it is usually mixed with an inert gas, such as carbon dioxide, nitrogen or one of the halogenated hydrocarbons, in a proportion of about 10% to perhaps 30% of ethylene oxide.
By reason of the cost of such gas mixtures, it is desirable to reuse them for as many cycles as possible, as is discussed in Satus U.S. Pat. No. 3,372,980; Ernst U.S. Pat. No. 3,549,312 and Skocypec et al U.S. Pat. No. 3,989,461.
However, with multiple sterilization cycles, the mixture acquires a small amount of air each time it is reused, so that the increasing proportion of air in the mixture after a number of reuse cycles produces a mixture which approaches the region of flammability. Satus solves the problem by venting the entire mixture before reaching the region of flammability and replacing it with an air-free mixture. Although this is effective from the standpoint of safety, it is expensive in its utilization of gas mixtures. Ernst and Skocypec et al both use flourinated hydrocarbons as their inert gas and recondense the ethylene oxide and inert gas for reuse, the air being separated during the condensation. These systems have the disadvantage of necessitating the use of relatively expensive inert gases which can be condensed to a liquid at relatively high temperatures. They are not economically feasible for low temperature condensing gases such as carbon dioxide and nitrogen which cannot be so readily condensed.
It is accordingly a major object of the present invention to provide a method for reuse of a mixture of ethylene oxide and an inert gas for an indefinite number of successive sterilization cycles without condensing the mixture.
It is another object of the invention to decrease the cost of gas sterilization.
It is still another object of the invention to provide for effective mixing of ethylene oxide and carbon dioxide.